Despite this - and the fact that the pair were on opposing sides of the subsequent Brexit vote - Mr McGuinness and Mrs Foster managed to forge a positive working relationship since they began sharing the OFMDFM portfolio.

In December, Mrs Foster insisted she had "nothing to hide" over the RHI scandal and refused to step down, but pressure mounted on Sinn Féin to act.

In January, Mr McGuinness said Mrs Foster should step aside as first minister to "allow a time-framed, comprehensive, independent investigation" into the RHI scheme. She refused.

So he instead resigned in protest against the DUP's handling of the debacle, sparking March's elections and Northern Ireland's current crisis.